Add Bcrypt support.

[baek-sang]

Any plan?

[samuel-lucas6]

Afraid not. bcrypt isn't in libsodium, only Argon2id, Argon2i, and scrypt are. Furthermore, bcrypt is weaker than Argon2 with decent parameters, and I intend to stick with one algorithm per purpose if possible.

Whilst bcrypt is stronger than Argon2 with lower parameters, it can't be used as a KDF, and there are weird restrictions on the password, so it's not very versatile.

[samuel-lucas6]

As an update, if libsodium implements bscrypt, that will probably be added and encouraged for password hashing instead of Argon2.